article: Three men traveling on a train began a conversition about the world's greatest wonders.
  " In my opinion," the first man said, " the Egyptian pyramids are the world's greatest wonder. Although they were built thousands of years ago, they are still standing. And remember: the people who built them had only simple tools. They didn't have the kind of machinery that builders and engineers have today.
  " I agree that the Egyptian pyramids are wonderful," the second man said, " But I don't think they're the greatest wonder. I believe computers are more wonderful than the pyramids. They have taken people to the moon and brought them back safely. They carry out mathematical calculations in seconds that would take a person a hundred years to do."
  He turned to the third man and asked, " What do you think is the greatest wonder in the world?"
  The third man thought for a long time, then he said, " Well, I agree that the pyramids are wonderful, and I agree that computers are wonderful, too. However, in my opinion, the most wonderful thing in the world is the thermos ."
  And he took a thermos out of his bag and held it up.
  The other two men were very surprised. " A thermos?" they exclaimed , " But that's a simple thing."
  " Oh, no, it's not," the third man said, " in the winter you put in a hot drink and it stays hot, in the summer you put in a cold drink and it stays cold. How does the thermos know whether it is winter or summer?"
question: The third man thought a thermos was the most wonderful thing in the world because   _  .
options: it lasted longer than the pyramids it cost less than a computer he thought it knew whether it was winter or summer the other two men were surprised when he told them about it